C++ Bug fixing: Hawaiian Pronunciation Program - c++

Question

I am writing a C++ program that will show you how to pronounce a Hawaiian word.
Rules:
p, k, h, l, m, n (Pronounced like the english versions.)
w -start of word (Either pronounced as a w or a v sound. We shall pronounce it as a w sound.)
w -after the letter ‘a’ (Either pronounced as a w or a v sound. We shall pronounce it as a w sound.)
w -after ‘i’ or ‘e’ (Pronounced as a v sound.)
w -after ‘u’ or o (Pronounced as a w sound.)
My progress: My program works, but there's a couple of bugs.
When I type "iwa", the pronunciation must be "ee-vah" but I'm
getting "ee-wah".
My code is not ignoring whitespaces. So when I type "e komo mai", I want "eh koh-moh meye" but instead, I get "e komo mai is pronounced eh-eh-koh-moh-oh-meye".
Here is my code:
#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
using namespace std;
string convertToHawaiian(string input);
bool vowelGroup(char first, char next, string& replacement);
bool consonantGroup(char prevchar, char currchar, string& replacement);
bool singleVowel(char current, string& replacement);
int main() {
// Declare my variables
string userInput;
string replacement;
//cout << "Enter a hawaiian word to pronounce ==>";
getline(cin,userInput);
// For loop that will call my Consonant function
// Call my Hawaiian function and put it
// into pronunciation
replacement = convertToHawaiian(userInput);
// if My initial input has a capital, the replacement
// will keep the capital letter at the beginning
if (isupper(userInput.at(0))) {
replacement.at(0) = toupper(replacement.at(0));
}
// Get rid of the '-' character at the end of the string
if (replacement.at(replacement.size() - 1) == '-') {
replacement.pop_back();
}
cout << userInput << " is pronounced " << replacement << endl;
return 0;
}
// My main function that will convert my input
// into the hawaiian pronunciation
string convertToHawaiian(string input) {
char nextChar;
string replacement = "";
string result = "";
// Iterate through my string to check for vowels,
// vowelgroups and consonants.
for (unsigned int i = 0; i < input.size(); i++) {
char character = input.at(i);
character = tolower(character);
if (i != input.size() - 1) {
nextChar = input.at(i + 1);
nextChar = tolower(nextChar);
}
if ((i != input.size() - 1) && (vowelGroup(character, nextChar, replacement))) {
i++;
result = result + replacement;
}
else if (singleVowel(character, replacement)) {
result = result + replacement;
}
else {
consonantGroup(character, nextChar, replacement);
result = result + replacement;
}
}
return result;
}
bool vowelGroup (char first, char nextChar, string& result) {
bool isVowel = true;
if (first == 'a') {
nextChar = tolower(nextChar);
if ((nextChar == 'i') || (nextChar == 'e')) {
result = "eye-";
}
else if ((nextChar == 'o') || (nextChar == 'u')) {
result = "ow-";
}
else {
return false;
}
}
else if (first == 'e') {
nextChar = tolower(nextChar);
if (nextChar == 'i') {
result = "ay-";
}
else if (nextChar == 'u') {
result = "eh-oo-";
}
else {
return false;
}
}
else if (first == 'i') {
nextChar = tolower(nextChar);
if (nextChar == 'u') {
result = "ew-";
}
else {
return false;
}
}
else if (first == 'o') {
nextChar = tolower(nextChar);
if (nextChar == 'i') {
result = "oy-";
}
else if (nextChar == 'u') {
result = "ow-";
}
else {
return false;
}
}
else if (first == 'u') {
nextChar = tolower(nextChar);
if (nextChar == 'i') {
result = "ooey-";
}
else {
return false;
}
}
else {
isVowel = false;
return isVowel;
}
return isVowel;
}
// Check to verify consonants
bool consonantGroup(char character, char nextChar, string& replacement) {
bool isConson = true;
if ((character == 'p') || (character == 'k') || (character == 'h') || (character == 'l') || (character == 'm') || (character == 'n')){
replacement = character;
return isConson;
}
if ((character == 'w') && (nextChar == 'a')) {
replacement = 'w';
return isConson;
}
else if (((character == 'u') || (character == 'o')) && (nextChar == 'w')) {
replacement = 'w';
cout << "Not replacing w" << endl;
return isConson;
}
else if (((character == 'i') || (character == 'e')) && (nextChar == 'w')) {
replacement = 'v';
return isConson;
}
else {
isConson = false;
return isConson;
}
}
bool singleVowel(char current, string& result) {
bool isVowel = true;
if (current == 'a') {
result = "ah-";
return isVowel;
}
else if (current == 'e') {
result = "eh-";
return isVowel;
}
else if (current == 'i') {
result = "ee-";
return isVowel;
}
else if (current == 'o') {
result = "oh-";
return isVowel;
}
else if (current == 'u') {
result = "oo-";
return isVowel;
}
else {
isVowel = false;
return isVowel;
}
}

Answer 1

One of the more common sources of bugs is shared mutable state.
In your case, it is state shared between loop iterations.
The whitespace case is handled here:
else {
consonantGroup(character, nextChar, replacement);
result = result + replacement;
}
and in that case, replacement will be string "spilled over" from the previous iteration.
The remedy is very simple: declare replacement inside the loop instead.
You can solve the "iwa" problem if you stare at these lines until you spot the bug:
if ((character == 'w') && (nextChar == 'a')) {
replacement = 'w';